Person

Simon the Zealot

One of the Twelve apostles, distinguished from Peter the Apostle (also Simon) by the epithet the Zealot (Greek Zēlōtēs, Luke 6:15; Acts 1:13) or the Aramaic equivalent the Cananaean (Kananaios, Matt 10:4; Mark 3:18, not "Canaanite" in the geographic sense; the term derives from Aramaic qan'ān, "zealous one"). Mentioned only in the apostolic lists; no narrative material in the Gospels. According to tradition, evangelized Persia and was martyred there, possibly with Jude Thaddaeus.

Biographical sketch

Name: Simon (Hebrew Shim'ōn), one of the most common Jewish names of the period; the distinguishing epithet was necessary.
"The Zealot": two possible meanings:
Member of the Zealot party, the militant Jewish nationalist movement that violently opposed Roman occupation, ultimately driving the AD 66-70 Jewish-Roman War. If this is the meaning, Simon was a converted insurgent: a member of the Twelve who came from the political-radical anti-Roman faction. This would put him alongside Matthew the Apostle (a tax-collector / Roman-collaborator) in the Twelve, with Jesus intentionally choosing apostles from opposite ends of the political spectrum.
"Zealous" as character trait, simply meaning he was passionate or fervent in religious devotion. Some scholarship prefers this reading because the term "Zealot" for the political party may post-date the apostolic generation (the named Zēlōtai faction emerges most clearly during the 66-70 war).
Either reading makes Simon a thematically significant figure: a man known for zeal, whether religious or political, who became an apostle under Jesus's teaching that the kingdom of God is not advanced by the sword (Matt 26:52).

Apostolic listings

Matt 10:4: "Simon the Cananaean"
Mark 3:18: "Simon the Cananaean"
Luke 6:15: "Simon who was called the Zealot"
Acts 1:13: "Simon the Zealot"

In all four lists, Simon is paired or grouped near Jude Thaddaeus / Judas son of James (and traditionally accompanies him in mission).

Post-resurrection ministry

No canonical material. Patristic and traditional sources offer multiple, sometimes-conflicting accounts:

Persia: the dominant tradition (preserved in the Western Roman martyrology and the Greek tradition) has Simon and Jude Thaddaeus preaching together in Persia / Mesopotamia, and being martyred there ~AD 65-80. Their feast is jointly celebrated on October 28 in Western Catholicism.
Egypt + Britain: a parallel tradition (preserved in some medieval Western sources) has Simon preaching in Egypt, then traveling to Britain in the company of Joseph of Arimathea, before returning east. The Britain leg is medieval-legendary and likely false.
Manner of death: variously given as crucifixion, sawing asunder (the most common iconographic depiction, Simon holding a saw), being struck down with a sword, or being killed with arrows.
Confidence level: the Persia tradition is patristic-attested; the manner of death is iconographic-traditional.

Theological themes

Zeal redirected

If Simon was indeed a member of the Zealot political party, his calling to apostleship is theologically significant:

Kingdom-not-of-this-world: Jesus's repeated insistence that His kingdom is not advanced by violent means (John 18:36; Matt 26:52). A converted Zealot apostle would have learned this conversion of zeal firsthand.
The mixed Twelve: a former tax collector (Matthew) and a former Zealot (Simon) in the same apostolic body demonstrates the gospel's ability to reconcile the irreconcilable. This is the political analog of Paul the Apostle's Jew-Gentile reconciliation theology.
Zealous of good works: Paul's later usage of zēlos / zēlōtēs language (Gal 1:14; Phil 3:6; Acts 22:3) and the conversion of zeal toward righteous ends (Tit 2:14; 1 Pet 3:13) may be partly informed by the apostolic memory of Simon's transformed zeal.

The hiddenness of faithful witness

Simon is one of several apostles (with James the Lesser, Bartholomew, Thomas in some respects) whose canonical narrative is bare and whose later tradition is thin. The pattern is itself theologically instructive: the apostolic foundation does not depend on every apostle being individually famous. The Twelve are a collective body; Simon's faithful but obscure witness is part of that body's testimony.